Determining width and height of electron spot

Abstract

A method in an X-ray source configured to emit, from an interaction region, X-ray radiation generated by an interaction between an electron beam and a target, the method including the steps of: providing the target; providing the electron beam; deflecting the electron beam along a first direction relative the target; detecting electrons indicative of the interaction between the electron beam and the target; determining a first extension of the electron beam on the target, along the first direction, based on the detected electrons and the deflection of the electron beam; detecting X-ray radiation generated by the interaction between the electron beam and the target; and determining a second extension of the electron beam on the target, along a second direction, based on the detected X-ray radiation.

Claims

1. A method in an X-ray source configured to emit, from an interaction region, X-ray radiation generated by an interaction between an electron beam and a target, the method comprising the steps of: providing the target; providing the electron beam; deflecting the electron beam along a first direction relative to the target; detecting electrons indicative of the interaction between the electron beam and the target; determining a first extension of the electron beam on the target, along the first direction, based on the detected electrons and the deflection of the electron beam; detecting X-ray radiation generated by the interaction between the electron beam and the target; and determining a second extension of the electron beam on the target, along a second direction, based on the detected X-ray radiation.

2. The method according to claim 1, wherein the target partially obscures a sensor area, the method further comprising: deflecting at least a part of the electron beam between the target and an unobscured portion of the sensor area.

3. The method according to claim 1, wherein the electron beam forms a spot on the target, the spot being wider in the first direction than in the second direction.

4. The method according to claim 1, wherein the first direction is substantially perpendicular to the second direction, and wherein the target is moving along the second direction.

5. The method according to claim 1, further comprising: adjusting, based on at least one of the determined first extension and the determined second extension of the electron beam, an intensity of the electron beam such that a power density supplied to the target is maintained below a predetermined limit.

6. The method according to claim 1, further comprising adjusting the electron beam such that the second extension of the electron beam on the target is decreased while the first extension of the electron beam on the target is maintained.

7. An X-ray source configured to emit X-ray radiation, comprising: a target; an electron source operable to generate an electron beam interacting with the target in an interaction region to generate X-ray radiation; electron-optics for controlling the electron beam; a first sensor adapted to detect electrons indicative of the interaction between the electron beam and the target; a second sensor adapted to detect X-ray radiation generated by the interaction between the electron beam and the target; and a controller operably connected to the first sensor, the second sensor and the electron-optics; wherein: the electron-optics is configured to deflect the electron beam in a first direction relative to the target; the controller is adapted to: determine a first extension of the electron beam on the target, along the first direction, based on the detected electrons and the deflection of the electron beam; and determine a second extension of the electron beam on the target, along a second direction, based on the detected X-ray radiation.

8. The X-ray source according to claim 7, wherein the target is a moving target configured to move along the second direction.

9. The X-ray source according to claim 8, wherein the second sensor is arranged to detect X-ray radiation propagating in a direction substantially perpendicular to the electron beam and the moving direction of the target.

10. The X-ray source according to claim 7, wherein the target is a liquid target propagating along the second direction.

11. The X-ray source according to claim 7, wherein said electron-optics is arranged to provide an elongated cross section of the electron beam on the target, wherein the largest diameter of the cross section is substantially parallel to the first direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described for the purpose of exemplification with reference to the accompanying drawings, on which:

(2) FIG. 1a is a schematic, cross sectional side view of an X-ray source according to some embodiments of the present invention.

(3) FIG. 1b is a schematic, perspective view of an X-ray source according to an embodiment comprising a liquid metal jet target;

(4) FIG. 2 is a schematic perspective view of an X-ray source according to an embodiment comprising a liquid metal jet target;

(5) FIGS. 3a and 3b illustrate different examples of an electron focal spot on a target according to embodiments of the present invention;

(6) FIG. 4 illustrate the relationship between an electron beam and X-ray radiation generated by the interaction between the electron beam and a target;

(7) FIG. 5 is a schematic representation of a system according to an embodiment; and

(8) FIG. 6 schematically illustrates a method according an embodiment.

(9) All figures are schematic, not necessarily to scale, and generally only show parts that are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION OF EMBODIMENTS

(10) Referring first to FIG. 1a, a cross sectional side view of an X-ray source 100a according to some embodiments of the present invention is illustrated. The X-ray source 100a comprises a target 110a here illustrated in the cross-sectional view by a circle. However, it is envisioned that the target 110a may assume other shapes or forms, and in particular it should be noted that the target 110a may be a liquid target, a rotating target, a solid target, or any other type of target capable of generating X-ray radiation by interaction with an electron beam.

(11) The X-ray source 100a further comprises an electron source 114a operable to generate an electron beam 116a travelling along an electron-optical axis and interacting with the target 110a to generate X-ray radiation. In the illustrated example, a first quantity of generated X-ray radiation 118a exits the X-ray source 100a in an exit direction along an axis that is substantially perpendicular to the electron-optical axis. A second quantity of generated X-ray radiation 119a travels in a direction being opposite the exit direction, towards an X-ray sensor 121a, i.e. a second sensor. The X-ray source 100a also comprises an electron detector 128a, i.e. a first sensor, configured to detect electrons indicative of the interaction between the electron beam and the target. In particular, the electron detector 128a is configured to receive at least part of the electron beam 116a passing the target 110a. The electron detector 128a is here arranged downstream of the target 110a with respect to the electron-optical axis. As is readily understood from the present disclosure, the first sensor, e.g. the electron detector 128a, may be arranged at other locations, and may be configured to detect e.g. backscattered electrons, secondary electrons, electrons passing the target 110a, electrons absorbed in the target 110a, and the like.

(12) Referring now to FIG. 1b, a cross sectional side view of an X-ray source according to an embodiment comprising a liquid metal jet target is illustrated. The illustrated X-ray source 100b utilizes a liquid jet 110b as a target for the electron beam. However, as is readily appreciated by the person skilled in the art, other types of targets, such as moving targets, or rotating solid targets, are equally possible within the scope of the inventive concept. Further, some of the disclosed features of the X-ray source 100b are merely included as possible examples, and may not be necessary for the operation of the X-ray source 100b.

(13) As indicated in FIG. 1b, a low pressure chamber, or vacuum chamber, 102b may be defined by an enclosure 104b and an X-ray transparent window 106b which separates the low pressure chamber 102b from the ambient atmosphere. The X-ray source 100b comprises a liquid jet generator 108b configured to form a liquid jet 110b moving along a flow axis F. The liquid jet generator 110b may comprise a nozzle through which liquid, such as e.g. liquid metal may be ejected to form the liquid jet 110b propagating towards and through an intersecting region 112b. The liquid jet 110b propagates through the intersecting region 112b towards a collecting arrangement 113b arranged below the liquid jet generator 108b with respect to the flow direction. The X ray source 100 further comprises an electron source 114b configured to provide an electron beam 116b directed towards the intersecting region 112b along an electron-optical axis. The electron source 114b may comprise a cathode for the generation of the electron beam 116b. In the intersecting region 112b, the electron beam 116b interacts with the liquid jet 110b to generate X-ray radiation 118b, which is transmitted out of the X-ray source 100b via the X-ray transparent window 106b. A first quantity of X-ray radiation 118b is here directed out of the X ray source 100b in an exit direction D.sub.1 substantially perpendicular to the direction of the electron beam 116b, i.e. the electron-optical axis, and the flow axis F.

(14) The liquid forming the liquid jet is collected by the collecting arrangement 113b, and is subsequently recirculated by a pump 120b via a recirculating path 122b to the liquid jet generator 108b, where the liquid may be reused to continuously generate the liquid jet 110b.

(15) Still referring to FIG. 1b, the X-ray source 100b here comprises an electron detector 128b, i.e. a first sensor, configured to receive at least part of the electron beam 116b passing the liquid jet 110b. The electron detector 128b is here arranged behind the intersecting region 112b as seen from a viewpoint of the electron source 114b. It is to be understood that the shape of the electron detector 128b is here merely schematically illustrated, and that other shapes of the electron detector 128b may be possible within the scope of the inventive concept. The X-ray source 100b also comprises an X-ray sensor 121b, i.e. a second sensor, configured to detect X-ray radiation generated by the interaction between the electron beam and the target. The X-ray sensor 121b is here arranged on an opposite side of the target 110b with respect to the X-ray window 106b. In particular, the X-ray sensor 121b may be arranged such that a second quantity of X-ray radiation 119b generated by the interaction between the electron beam 116b and the target 100b, in a direction D.sub.2 being substantially perpendicular to the flow axis F and the electron-optical axis, may reach the X-ray sensor 121b.

(16) Referring now to FIG. 2, a schematic perspective view of an X-ray source 200 according to an embodiment comprising a liquid metal jet target is illustrated. The illustrated X-ray source 200 utilizes a liquid jet 200 as a target for the electron beam. However, as is readily appreciated by the person skilled in the art, other types of targets, such as moving targets, or rotating solid targets, are equally possible within the scope of the inventive concept. Further, some of the disclosed features of the X-ray source 200 are merely included as possible examples, and may not be necessary for the operation of the X-ray source 200.

(17) The X-ray source 200 generally comprises an electron source 214, 246, and a liquid jet generator 208 configured to form a liquid jet 210 acting as an electron target. The components of the X-ray source 200 is located in a gas-tight housing 242, with possible exceptions for a power supply 244 and a controller 247, which may be located outside the housing 242 as shown in the drawing. Various electron-optical components functioning by electromagnetic interaction may also be located outside the housing 242 if the latter does not screen off electromagnetic fields to any significant extent. Accordingly, such electron-optical components may be located outside the vacuum region if the housing 242 is made of a material with low magnetic permeability, e.g., austenitic stainless steel.

(18) The electron source generally comprises a cathode 214 which is powered by the power supply 244 an includes an electron emitter 246, e.g. a thermionic, thermal-field or cold-field charged-particle source. Typically, the electron energy may range from about 5 keV to about 500 keV. An electron beam from the electron source is accelerated towards an accelerating aperture 248, at which point it enters an electron-optical system comprising an arrangement of aligning plates 250, lenses 252 and an arrangement of deflection plates 254. Variable properties of the aligning plates 250, lenses 252, and deflection plates 254 are controllable by signals provided by the controller 247. In the illustrated example, the deflection and alignment plates 250, 254 are operable to accelerate the electron beam in at least two transversal directions. After initial calibration, the aligning plates 250 are typically maintained at a constant setting throughout a work cycle of the X-ray source 200, while the deflection plates 254 are used for dynamically scanning or adjusting an electron spot location during use of the X-ray source 200. Controllable properties of the lenses 252 include their respective focusing powers (focal lengths). Although the drawing symbolically depicts the aligning, focusing and deflecting means in a way to suggest that they are of the electrostatic type, the invention may equally well be embodied by using electromagnetic equipment or a mixture of electrostatic and electromagnetic electron-optical components. The X-ray source may comprise stigmator coils 253 which may provide for that a non-circular shape of the electron spot is achieved.

(19) Downstream of the electron-optical system, an outgoing electron beam I.sub.2 intersects with the liquid jet 210 in an intersecting region 212. This is where the X-ray production may take place. X-ray radiation may be led out from the housing 242 in a direction not coinciding with the electron beam. Any portion of the electron beam I.sub.2 that continues past the intersecting region 212 may reach an electron detector 228. In the illustrated example, the electron detector 228 is simply a conductive plate connected to earth via an ammeter 256, which provides an approximate measure of the total current carried by the electron beam I.sub.2 downstream of the intersecting region 212. As the figure shows, the electron detector 228 is located a distance D away from the intersecting region 212, and so does not interfere with the regular operation of the X-ray source 200. Between the electron detector 228 and the housing 242, there is electrical insulation, such that a difference in electrical potential between the electron detector 228 and the housing 242 can be allowed. Although the electron detector 228 is shown to project out from the inner wall of the housing 242, it should be understood that the electron detector 228 could also be mounted flush with the housing wall. The electron detector may further be equipped with an aperture arranged so that electron impinging inside the aperture may be registered by the electron detector whereas electrons impinging outside of the aperture may not be detected.

(20) A lower portion of the housing 242, a vacuum pump or similar means for evacuating gas molecules from the housing 242, receptacles and pumps for collecting and recirculating the liquid jet are not shown on this drawing. It is also understood that the controller 247 has access to the actual signal from the ammeter 256.

(21) The X-ray source 200 may further comprise an X-ray transparent window (not shown) and an X-ray detector (not shown) similar to components 106b and 121b in FIG. 1b. The electron-optical system described may be used to adjust the electron beam extension based on measurement from the electron detector 228 and/or the X-ray detector (not shown). By adjusting both the focusing lens 252 and the stigmator coils 253 the electron width of the electron focal spot may be adjusted independently in directions along and perpendicularly to the flow direction of liquid jet 210.

(22) Referring now to FIGS. 3a and 3b, different examples of an electron focal spot on a target according to embodiments of the present invention are illustrated.

(23) In FIG. 3a, a non-circular electron focal spot 358a is shown on a target 310a. The electron focal spot 358a is here oriented such that its longest extension, here a width 360a, is arranged along a direction being perpendicular to a direction of travel T of the target 310a. The narrowest or shortest extension of the electron focal spot 358a, here the length 362a, is arranged along the direction of travel T. Such an arrangement may allow for a relatively high total power of the electron beam to be used without overheating the target 310a. The width 360a may be at least twice as long as the length 362a, such as at least four time as long. In an embodiment the width 360a may be between 40 μm and 80 μm correspondingly the length 362a may be between 10 μm and 20 μm. Different combinations within these intervals may be used to an advantage.

(24) In FIG. 3b, a non-circular electron focal spot 358b is shown on a target 310b. The electron focal spot 358b is here oriented such that its shortest extension, here a width 360b, is arranged along a direction being perpendicular to a direction of travel T of the target 310b. The most broad or longest extension of the electron focal spot 358b, here the length 362b, is arranged along the direction of travel T. Such an arrangement may apply an unnecessary load on the target 310b, which increases the risk of overheating the target 310b at a given total power of the electron beam compared to the arrangement disclosed in conjunction with FIG. 3a.

(25) Referring now to FIG. 4, an example of the relationship between an electron focal spot size 458 and X-ray radiation generated by the interaction between the electron beam and a target, i.e. the interaction region 464, is illustrated. It should be noted that this figure is not necessarily drawn to scale, and that the shapes of the illustrated features are not limiting but merely an example of possible shapes. It should further be noted that the illustrated example is merely one way of defining the electron focal spot size and the interaction region wherein X-ray radiation is generated, and that other definitions may be made without departing from the scope of the present inventive concept.

(26) Part of a target 410 is shown, whereon an electron focal spot size 458 and an interaction region 468 are illustrated. It may be noted that the interaction region 468 and the electron focal spot size 458 are overlapping. The graph below the target 410 illustrate properties of an intensity distribution of the electron beam along the line A-A indicated on the target 410.

(27) As defined in the present disclosure, the interaction region 468 corresponds to the full width at half maximum Imax of the intensity distribution. Also, as illustrated by the shaded area 470, some electrons do not contribute to the generation of X-ray radiation and may in some respects be deemed wasted. The area 470 under the graph 472 reflect the power of electrons that do not contribute to the generation of X-ray radiation. Similarly, the area 474 under the graph 472 reflect the power of electrons that contribute to the generation of X-ray radiation.

(28) Referring now to FIG. 5, a schematic representation of an X-ray source 500 according to an embodiment is illustrated. The X-ray source 500 comprises a first sensor 578 adapted to detect electrons indicative of the interaction between the electron beam and the target, a second sensor 580 adapted to detect X-ray radiation generated by the interaction between the electron beam and the target, and a controller 547 operably connected to the first sensor, the second sensor and electron-optical means (not illustrated).

(29) A method in an X-ray source according to the inventive concept will now be described with reference to FIG. 6. For clarity and simplicity, the method will be described in terms of ‘steps’. It is emphasized that steps are not necessarily processes that are delimited in time or separate from each other, and more than one ‘step’ may be performed at the same time in a parallel fashion.

(30) The method in the X-ray source configured to emit, from an interaction region, X-ray radiation generated by an interaction between an electron beam and a target, comprises the step 682 of providing the target, the step 684 of providing the electron beam, the step 686 of deflecting the electron beam along a first direction relative the target, the step 688 of detecting electrons indicative of the interaction between the electron beam and the target, the step 690 of determining a first extension of the electron beam on the target, along the first direction, based on the detected electrons and the deflection of the electron beam, the step 692 of detecting X-ray radiation generated by the interaction between the electron beam and the target, and the step 694 of determining a second extension of the electron beam on the target, along a second direction, based on the detected X-ray radiation.

(31) The person skilled in the art by no means is limited to the example embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. In particular, X-ray sources and systems comprising more than one target or more than one electron beam are conceivable within the scope of the present inventive concept. Furthermore, X-ray sources of the type described herein may advantageously be combined with X-ray optics and/or detectors tailored to specific applications exemplified by but not limited to medical diagnosis, non-destructive testing, lithography, crystal analysis, microscopy, materials science, microscopy surface physics, protein structure determination by X-ray diffraction, X-ray photo spectroscopy (XPS), critical dimension small angle X-ray scattering (CD-SAXS), and X-ray fluorescence (XRF). Additionally, variation to the disclosed examples can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.